Post-mortem multilevel analysis in the visual cortex of CDKL5 deficiency disorder patients

CDKL5 Deficiency Disorder (CDD) is an X-linked neurodevelopmental disease caused by mutations of the CDKL5 gene. CDD patients exhibit a wide spectrum of clinical manifestations mostly recapitulated by CDD murine models, such as severe intellectual disability, early onset epilepsy, hypotonia, autistic-like traits and sensory abnormalities (i.e. cortical visual impairments). Studies performed in in murine models of CDD revealed a crucial role of this serine/threonine kinase in the cellular and molecular organization of both excitatory and inhibitory circuitry in the cerebral cortex including the formation and stabilization of dendritic spines and the organization of parvalbumin (PV)+ interneurons. However, whether similar changes affect the cerebral cortex of CDD human patients is still unknown. Here, we investigate the consequences of CDKL5 mutations in the only two available post-mortem CDD brains specimens by analysing both the cellular and synaptic organization of the human cortex. Moreover, we also assess putative epigenetic modifications in these patients by investigating the expression of a specific methylation on histone H3. Since visual deficits are a key sign of CDD and represent a promising biomarker for both preclinical and clinical studies, we focused our analyses in the primary visual cortex (i.e.: BA17). In this study, we applied both immunohistochemistry and western blotting analyses which show that in both CDD patients there are profound alterations of the overall cortical cytoarchitecture and, in particular, in the density of parvalbumin (PV)+ interneurons compared to neurotypical age- and sex-matched individuals. Importantly, we report severe impairments both in structural and functional components of the glutamatergic synapse. Finally, we find that the expression of methylated (K9me3+) H3 is robustly reduced in tissue from CDD patients. This is the first study, to our knowledge, that describes putative neuronal/synaptic and epigenetic modifications affecting the primary visual cortex of CDD patients, likely underlying visual impairments typical of this condition. Moreover, our work provides further support to the idea that CDKL5-KO mice represent a high-face validity model of CDD because they recapitulate the neuronal alterations found in humans.